The air distribution within the clean room must provide the room with the required supply and extract airflow rates, while having minimal impact on the room itself.
The method of air supply and extract chosen will depend on the type and grade (class) of clean room required. Low-grade rooms will tend to have air supplied at a high level via ceiling diffusers and low-level extract through sidewall grilles. The aim is to thoroughly mix the room air with incoming clean air to achieve the required air particulate level by dilution.
Higher-grade rooms requiring unidirectional airflow require more complex arrangements. Ideally rooms requiring horizontal flow should have the supply air delivered via an "air wall," complete with terminal filters and extracted via perforated panels in the opposite wall.
Rooms requiring vertical flow have the supply air delivered via a proprietary clean-room ceiling complete with supply air filters and ideally extracted via a false floor plenum.
However, false floors are unacceptable in some applications, e.g., pharmaceutical process rooms, due to the problems they pose with cleaning, and a compromise is needed.
Normally, low-level extract is provided, ideally by means of a continuous slot, or row, of extract grilles. As a minimum requirement these slots or grilles should be positioned in the two longest opposite walls of a rectangular room. It should be noted that, if the distance between these walls is greater than four metres, there will be a tendency to pull the air flow toward the walls (out of the vertical) at the working plane level, which may well be unacceptable.
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